Final answer:
Argentinosaurus was in the Sauropodomorpha group of dinosaurs called Saurischia, also known as the "lizard-hipped" dinosaurs.
Step-by-step explanation:
Argentinosaurus belonged to the family of dinosaurs called Saurischia, also known as the "lizard-hipped" dinosaurs.
This family has a simple, three-pronged pelvis. Saurischia is further divided into two groups: the Theropoda, which includes the carnivorous dinosaurs like Tyrannosaurus rex, and the Sauropodomorpha, which contains the long-necked herbivorous dinosaurs like Argentinosaurus.
So, Argentinosaurus was in the Sauropodomorpha group of dinosaurs.